Topography and axonal collaterals of trigeminocerebellar projection to the paramedian lobule and uvula in the rabbit cerebellum

To study projections of the trigeminal sensory nuclei (TSN) to the rostral parts of the paramedian lobule (PML) and of the uvula of the rabbit cerebellar cortex, the retrograde double fluorescent labeling method was used. Injections of Fast Blue (FB) into PML and Diamidino Yellow (DY) into the uvula, resulted in prominent labeling neurons with FB bilaterally and with DY ipsilaterally, in the principal trigeminal nucleus, subnucleus oralis, and rostral and caudal subnucleus interpolaris. We observed topographical arrangement of neurons in such a fashion that FB labeled cells were localized in the medial and DY labeled cells in the lateral regions of TSN. Apart from this small number of double FB+DY labeled neurons (n = 138) were found in the narrow common region of single labeling. This implies that PML and the uvula receive independent trigeminal sensory information from neurons in separate regions of TSN. However, some trigeminal neurons may also exert simultaneous influences upon these hemispheral and vermal components by way of axonal branchings.     

The projection of splanchnic afferents on the cerebellum of the cat

1. The projections of the ipsilateral and contralateral splanchnic nerves on the cerebellum were studied in cats under sodium thiopentone anaesthesia.2. The splanchnic nerves were electrically stimulated. Evoked potentials and single unit discharges were recorded by means of 2.5 M-NaCl-filled glass micropipettes. A responsive region was found in the intermediate cortex of lobules Vb to f of the anterior lobe.3. The Agammadelta fibres of the splanchnic nerve had a bilateral cerebellar representation. The Abeta fibres were represented only on the ipsilateral side.4. At the level of the upper cervical spinal cord, fibres from the ipsilateral splanchnic nerve were conveyed in both the dorsal and lateral funiculi; fibres from the contralateral nerve were restricted to the ipsilateral lateral funiculus.5. On the basis of the characteristic potential fields generated in the cerebellar cortex, it is concluded that the majority of the splanchnic afferents studied terminate in the cerebellum as climbing fibres. A few responses of short latency may have been due to a mossy fibre input.6. In interaction experiments, a conditioning stimulus to one splanchnic nerve depressed the response to stimulation of the other nerve for up to 80-100 msec, the effect being most pronounced at 40-50 msec. During this period, spontaneous activity of the cerebellar unit was also suppressed.7. The organization of the splanchnic pathways to the cerebellum and their terminal connexions are discussed.     

The projection from the nucleus reticularis tegmenti pontis to the cerebellum in the rhesus monkey

Summary Following injections of horseradish peroxidase in various parts of the monkey cerebellum, the distribution of labelled cells in the nucleus reticularis tegmenti pontis (NRT) has been studied. As a rule, labelled cells are found at all rostrocaudal levels of the NRT regardless of the injection size and site. The densest projection from NRT seems to reach the vermal visual area (lobulus VII), a less dense projection supplies the anterior lobe while the paramedian lobule receives a more sparse projection than the anterior lobe. Very few labelled cells were found in the NRT after injections of crus I and II. The projection is topographically organized so that the dorsomedial part of the NRT supplies lobulus VII, a large central region sends fibres to the anterior lobe (and the cerebellar hemispheres), while the lateral extension of NRT (processus tegmentosus lateralis) is connected with the paramedian lobule.The results of the present study are compared with those of a preceding one of cortical afferents to NRT. It is concluded that the cortical areas projecting to the NRT seem likely to exert their influences on largely different parts of the cerebellum via the NRT. The present results are also discussed inrelation to termination of other afferent contingents in the NRT, and it is concluded that the NRT is not homogenous anatomically, and consequently different parts of the nucleus would be expected to play somewhat different functional roles.     

A direct projection from the cerebellum to the telencephalon in the goldfish, Carassius auratus

Recent studies showed that the cerebellum is involved in cognitive functions previously thought to be located in the telencephalon only. Various indirect connections between telencephalon and cerebellum are long known and may be the basis for the interaction of these two brain areas. By means of biotinylated dextran amine injections into the telencephalon and cerebellum in the goldfish, Carassius auratus, we found a direct projection from the valvula cerebelli to the telencephalon. Together with other studies in fish, birds, and mammals, these data suggest that direct connections between cerebellum and telencephalon are more common than previously thought and may contribute to the integration of telencephalic and cerebellar functions.     

Postnatal development and synapse elimination of climbing fiber to Purkinje cell projection in the cerebellum

Cerebellar climbing fiber (CF) to Purkinje cell (PC) synapses in rodents provides a good model to study mechanisms underlying postnatal development of synaptic functions and elimination of redundant synapses in the central nervous system. At birth, each PC is innervated by multiple CFs. Then, single CF input is selected, matured and strengthened, while surplus CFs are eliminated. By the end of the third postnatal week, most PCs become innervated by single CFs. This up-date article aims to provide an overview of recent studies on the mechanisms of this process.     

Stimulation of the rabbit hypothalamus: caudal projections to respiratory and cardiovascular centres.

1. Electrical stimulation of a small area of the hypothalamus, lying about 2 mm dorsal to the lateral margin of the mammillary bodies, evoked a characteristic complex of effects in the anaesthetized rabbit. 2. The observed effects included apneusis followed by tachypnoea, increased arterial blood pressure, and vagally mediated bradycardia. Exophthalmost and pupillodilatation was commonly seen. The ears were erected and the vibrissae drawn forward. Somatic effects were weaker, but often included increased extensor tone, especially in the forelimbs. 3. The intensity of these effects was dependent upon the frequency of stimuli within the trains. Effects were weak or absent below 20 shocks/sec, and were near-maximal above 60 shocks/sec, when employing constant-current rectangular wave stimuli of 100-300 muA, 1 msec pulse duration and 5-9 sec train duration. 4. The effects were not dependent upon connexions with the cerebral cortex, but were mediated by pathways that projected ipsilaterally from each side of the hypothalamus through the mesencephalon. 5. The evidence suggests that this region of the rabbit hypothalamus is partly homologous with that hypothalamic area associated with the defence reaction in cat. However, the over-all responses to stimulation in the anaesthetized rabbit differed considerably from those described in the anaesthetized carnivore, suggesting that their integrated physiological responses to emotional threat are dissimilar.     

The projection from nucleus reticularis tegmenti pontis onto the cerebellum in the cat

Summary Following stereotactically performed lesions in nucleus reticularis tegmenti pontis (N.r.t.) degenerating fibers are traced to the contralateral N.r.t., to the pontine nuclei, through brachium pontis to restricted areas of the cerebellar nuclei and to most parts of the cerebellar cortex where they terminate in the granular layer. Most degenerating fragments are found in the contralateral half of the cerebellum with the greatest density in the vermal lobules VI and VIIA and in the flocculus.Following injections of HRP in the various cerebellar lobules labeled cells are mainly present within limited groups in the N.r.t.. Injections in vermal lobules VI-VIII B give rise to labeled cells within circumscribed areas in the dorsal and ventral parts throughout the rostrocaudal extent of the N.r.t.. In cases with injections in lobule IX or the ventral paraflocculus labeled cells are found ventrally in the rostral half of the N.r.t., while following injections in the vermal lobules I-V labeled cells are mainly found in the ventral and caudal part of the N.r.t.. Following injections in the intermediate and lateral parts of the anterior lobe, Crus I and II, the paramedian lobule and the dorsal paraflocculus labeled cells occur within groups in medial and lateral parts throughout the rostrocaudal extent of the N.r.t.. Following injections in the flocculus labeled cells are found in a very distinct group in the dorsal and rostral part of the N.r.t., While an injection in the nodulus (lobule X) gave rise to a smaller group of labeled neurons in the dorsolateral corner in the caudal part of the N.r.t.. Labeled cells within processus tegmentosus lateralis (p.t.l.) are only found following injections in lobules VI-VIIIA, Crus I and II and the dorsal paraflocculus.From what is known about afferents to the N.r.t., it is concluded that no cerebellar lobule gets information from one only of these sources via the N.r.t.. Visual information can probably be mediated from the superior colliculus via the N.r.t. to the flocculus and to a minor extent to the vermal lobules VI-VIII B, and from the pretectum via the N.r.t. to both vermal and lateral parts of the cerebellum.     

辣根过氧化物酶逆行标记鸡小脑向海马结构的直接投射

目的:观察鸡是否存在小脑向海马的直接投射.方法:将30%辣根过氧化物酶水溶液注射到鸡一侧端脑的海马结构,逆行追踪双侧端脑和小脑向海马结构的传入纤维联系.结果:在小脑,第Ⅰ～Ⅵ叶、Ⅹ叶和Ⅸ叶的前半叶皮质中的蒲氏细胞被标记.在端脑,双侧的外侧隔核、海马结构的旁海马内侧区(APHm)均有多量神经元被标记,初步表明禽类海马结构在端脑的传入联系类似于哺乳类.结论:鸡小脑蒲氏细胞存在向端脑海马结构的直接投射.     

Parasagittal zonal pattern of olivo-nodular projections in rabbit cerebellum

Injection of horseradish peroxidase (HRP) into the nodulus of the rabbit retrogradely labeled cells in 5 subdivisions of the contralateral inferior olive. Localized HRP injections at each of the medial, intermediate and lateral parts of the nodulus revealed 6 longitudinal zones, two zones in each part, projected differentially from the 5 olivary subdivisions: (i) the medial-most zone projected from the beta nucleus, (ii) the lateral zone of the medial part and (iii) the lateral zone of the intermediate part both from the dorsal cap, (iv) the medial zone of the intermediate part from the ventrolateral outgrowth, (v) the medial zone of the lateral part from the dorsomedial cell column, and (vi) the lateral-most zone from the rostrolateral part of the medial accessory olive. A complication is that the zones (v) and (vi) seemed to cover the dorsal lamina of the nodulus, but not the ventral lamina. The lateral part of the ventral nodulus seemed to be projected from the dorsal cap and may therefore be a lateral extension of zone (iv). There was an indication that the rostral-most area of the medial accessory olive also projects to the nodulus, but a specific receptive zone for this projection was unclear. The present results suggest that the small lateral area of the nodulus previously found to be involved in cardiovascular control is projected from the rostrolateral part of the medial accessory olive and/or the dorsomedial cell column.     

Axonal projection patterns visualized with horseradish peroxidase in organized cultures of cerebellum

Neurons of the cerebellum and brain stem region of organotypic cultures were injected intracellularly with horseradish peroxidase. The axonal pattern was analyzed for the three cell types studied—Purkinje neurons, deep cerebellar neurons, and brain stem neurons. There was a consistent pattern for each cell type. The axon of the Purkinje neuron was uniform in diameter throughout, sometimes with one recurrent collateral, and within the deep nuclear region branched to produce a terminal field with many axon bulbs measuring 2–4 μm in diameter. The deep cerebellar neuron gave rise to a single axon which branched into a number of major axons, most of which coursed for long distances along the margin of the cortical region. Where the cortical region was separated off from the deep nuclear area, the axon of the deep cerebellar neuron branched and many axons coursed through the intervening zone to the cortex. The terminals in the cortical region were seen either as expansions along the fibre or as grape-like clusters on small side branches of the axons. The brain stem neuron had multiple axons which branched profusely and produced a system of fine-calibre varicose fibres, many of which coursed far into the outgrowth region.This study characterized the distribution of the axons of each neuron type. The results corroborate the fibre patterns seen in the living, stained and fluorescence studies of these cultures. The axon pattern for each neuron type resembles that of the corresponding neuron in the animal. These results will be correlated with the electrophysiological studies of the connections formed by the same neurons in sister cultures.     

Olivocerebellar modulation of motor cortex ability to generate vibrissal movements in rat

The vibrissal movements known as whisking are generated in a pulsatile, or non-continuous, fashion and comprise sequences of brief regularly spaced movements. These rhythmic timing sequences imply the existence of periodically issued motor commands. As inferior olivary (IO) neurones generate periodic synchronous discharges that could provide the underlying timing signal, this possibility was tested by determining whether the olivocerebellar system modulates motor cortex (MCtx)-triggered whisker movements in rats. Trains of current pulses were applied to MCtx, and the resulting whisker movements were recorded using a high speed video camera. The evoked movement patterns demonstrated properties consistent with the existence of an oscillatory motor driving rhythm. In particular, movement amplitude showed a bell-shaped dependence on stimulus frequency, with a peak at 11.5 ± 2.3 Hz. Moreover, movement trajectories showed harmonic and subharmonic entrainment patterns within specific stimulus frequency ranges. By contrast, movements evoked by facial nerve stimulation showed no such frequency-dependent properties. To test whether the IO was the oscillator in question, IO neuronal properties were modified in vivo by intra-IO picrotoxin injection, which enhances synchronous oscillatory IO activity and reduces its natural frequency. The ensuing changes in the evoked whisker patterns were consistent with these pharmacological effects. Furthermore, in cerebellectomized rats, oscillatory modulation of MCtx-evoked movements was greatly reduced, and intra-IO picrotoxin injections did not affect the evoked movement patterns. Additionally, multielectrode recording of Purkinje cell complex spikes showed a temporal correlation of olivocerebellar activity during MCtx stimulus trains to evoked movement patterns. In sum, the results indicate that MCtx's ability to generate movements is modulated by an oscillatory signal arising in the olivocerebellar system.     

鸡小脑浦肯野细胞向海马的直接投射-透射电镜观察

目的:进一步观察和确定前期的鸡小脑浦肯野细胞向端脑海马结构的直接投射.方法:选择2月龄左右的青年鸡,外科方法开颅,直流电损毁小脑V叶白质或红藻氨酸选择性损毁Ⅵa的浦肯野细胞和颗粒细胞,动物存活7 d,透射电镜观察端脑海马结构的旁海马内侧区(APHm)超微结构的变化.结果:于APHm内出现变性纤维及变性终末,以泡沫型变性最为普遍,并可见到变性终末与APHm内神经元形成突触联系.结论:鸡小脑浦肯野细胞可直接投射向海马结构,并与APHm神经元形成单突触联系.     

Somatotopical organization of the projection from the nucleus interpositus anterior of the cerebellum to the red nucleus. An experimental study in the cat with silver impregnation methods

Summary Small lesions were done in various areas of the nucleus interpositus anterior (NIA) of the cerebellum, and the distribution of terminal degeneration was studied in the red nucleus with the methods of Nauta and Glees. The NIA projects to the contralateral red nucleus. Two principles of organization can be demonstrated in the projection: a caudorostral arrangement in the red nucleus corresponds to a mediolateral organization in the NIA and a mediolateral arrangement in the red nucleus corresponds to a caudorostral organization of the NIA. The latter distribution coincides with the somatotopical areas of the red nucleus defined by Pompeiano and Brodal (1957). Special attention has been paid to the questions of the subdivision of the cerebellar nuclei and of the course of the fibres issuing from the nuclei in the cerebellar hilus. The present findings on the projection of the NIA to the red nucleus have been correlated with recent anatomical and physiological data on the cerebellum and the red nucleus.Abbreviations BC brachium conjunctivum - c caudal - d dorsal - Ext extensor effects - Flex flexor effects - forel forelimb area - HB hook-bundle - Hb. P habenulo-peduncular tract - hindl hindlimb area - I lateral - m medial - NF nucleus fastigii or medialis - NIA nucleus interpositus anterior - NIP nucleus interpositus posterior - NL nucleus lateralis - r rostral - v ventral - III root fibres of the third nerve - IV fourth ventricle Fellow of the Canadian Medical Research Council.     

Zonal organization of cortico-nuclear and nucleo-cortical projections of the paramedian lobule of the cat cerebellum. 2. The C2 zone

 The cortico-nuclear (C-N) and nucleo-cortical (N-C) projections of the C₂ cortical zone in pars anterior (pa) and pars posterior (pp) of the paramedian lobule (PML) in the posterior lobe of the cat cerebellum were investigated with a combined electrophysiological and neuroanatomical technique. In each experiment the medio-lateral boundaries of the zone were localized on the cortical surface by recording field potentials mediated via climbing fibres and evoked in the zone by activity elicited in spino-olivocerebellar paths through percutaneous stimulation of the fore- and hindlimbs; a small (15–30 nl) injection of 1–2% WGA-HRP was then made into the zone. Distributions in the deep cerebellar nuclei were determined with light microscopy both for C-N terminal labelling due to anterograde axonal transport by Purkinje cells and for cell bodies labelled due to retrograde transport in N-C axons. The extent to which retrogradely labelled olivary neurones were confined to the part of the rostral medial accessory olive that innervates the C₂ zone was estimated to provide an indication of the degree to which the injected tracer might have spread beyond the boundaries of the zone. The C-N projection from the part of the C₂ zone in PML pa terminates almost exclusively (probably exclusively) in nucleus interpositus posterior (NIP) at all medio-lateral levels of the nucleus but most extensively at middle and lateral levels. At most levels the C-N termination territory forms a crescent with its outer curve following the caudal, dorsal and rostral borders of the nucleus and as a result it is mainly in the dorsal half of the nucleus. There is heavy overlap with the projection from the lobule V part of the C₂ zone previously studied by us. The projection from the C₂ zone in PML pp terminates entirely in NIP, but although at middle medio-lateral levels in the nucleus there is substantial overlap with the PML pa and lobule V projections, the projection territory is confined to the medial half of the nucleus. Evidence was obtained compatible with the view that throughout the C₂ zone its lateral and medial parts project to different parts of NIP. In both PML pa and pp the C₂ zone receives N-C projections from NIP. Most of the N-C cells concerned are in the dorsal half of NIP and the great majority lie within the corresponding C-N projection territory. However, the N-C projection to PML pa appears c. 6 times heavier than that to PML pp and the PML pa part of the zone also receives a minor additional projection from nucleus lateralis (NL). The findings are discussed in relation to the hypothesis of olivo-cortico-nuclear complexes or compartments, with particular reference to the internal organization of the C₂ complex. Received: 28 April 1997 / Accepted: 22 July 1997     

Axonal ramification of neurons in the nucleus reticularis tegmenti pontis projecting to the paramedian lobule in the rabbit cerebellum

Projections of the nucleus reticularis tegmenti pontis (NRTP) to the cerebellar paramedian lobule were examined in the rabbit by means of the double fluorescent retrograde tract-tracing method. The rabbit NRTP is composed of a medial, large part comprising zones A (dorsomedial), B (central) and C (lateral), and of a lateral, small part (the processus tegmentosus lateralis; PTL). Following unilateral injections of Fast Blue (FB) into the rostral part of the paramedian lobule (rPML) and of Diamidino Yellow (DY) into the caudal part (cPML), known to receive spinal inputs from forelimb and hindlimb, respectively, substantial numbers of single labeled neurons were found in all bilateral NRTP divisions, apart from the zone C. Most projection neurons to the PML were located in the medial and medioventral regions of the zone B. Smaller numbers of projection neurons were located in the PTL, zone A and outside the zone B among fibers of the medial lemniscus. The pattern of FB and DY labeling suggested that neurons projecting to the rPML and cPML originated in common rather than separate regions within the NRTP. In addition, a small percentage (mean 1.3%) of double FB+DY labeled neurons were detected with a clear contralateral preponderance, among single labeled FB or DY cells. In spite of the rarity, all the NRTP neurons giving rise to intralobular collateral projections can be regarded as potential sources of simultaneous modulating influences upon two functional different forelimb (rPML) and hindlimb (cPML) regions. The findings have been discussed in relation to earlier studies in other species and commented on with respect to the possible functional meaning of these projections.